My invention relates to an improved overload protection apparatus for hydraulic multi-function equipment which senses overpressure conditions in a fluid system and interrupts equipment usage until an unsafe condition is corrected.
The present invention is directed to hydraulic systems particularly used on utility type trucks such as derrick diggers or the like. Such equipment usually incorporates a single hydraulic pump and several units of operating equipment such as a winch, a digger, an extension cylinder and a lift cylinder, each controlled by an open center control valve adapting the units for bidirectional operation. The control valves are normally teed off of a common manifold and share a common return to a tank or reservoir.
The hazard associated with equipment of this type is the occurrence of an overpressure condition in the boom cylinder which can seriously damage the derrick or boom of the unit. Such an overstress condition occurs when the boom is overloaded from using either a winch on a larger than rated load at given orientation or extending the extension cylinder beyond limits while fully loaded or operating the auger in a too soft soil condition with the boom extended. Under any of these situations a normal lift cylinder pressure may be exceeded, causing boom damage and hydraulic equipment failure. Attempts to control the overpressure condition by putting a relief valve on a holding valve for the particular unit is not a satisfactory solution since it can cause a loss of holding power, sacrifice equipment operation and create an additional operator safety concern.